Hi !!
Is is sufficient to have following:
example.com. IN TXT "v=spf1 ip4:192.168.1.1 -all"
mxsender.example.com. IN TXT "v=spf1 ip4:192.168.1.1 -all"
And configure your MTA at 192.168.1.1 to say "HELO mxsender.example.com"
instead of "HELO example.com". Mail not from 192.168.1.1 is forged anyway,
whether is says "HELO example.com" or not.
this does not prevent anyone to use HELO example.com
--
BEst regards ...
It's a fine line between fishing & standing still
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